Patent GB-524752-A (GB)
Title: Improvements in the tuning mechanism of radio-receivers
IPC: H03J5/14
Filed: 1939-02-06
Abstract: 524,752. Electric control systems. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPEN-FABRIEKEN. Feb. 6, 1939, No. 3897. Convention date Feb. 8, 1938. [Class 40 (i)] [Also in Group XL] In a wireless receiver tuned to a number of predetermined stations by a keyboard or the like, a brake, electro-magnetically controlled from a highly selective channel, is provided together with switch means such that the operation of the brake is only prepared over a limited range. The operation of button T1, with contacts as shown in Fig. 1, energizes relay B to change over its contacts consequent on the removal of the short circuit through contact b4 and the previously depressed button T2 which is released by the depression of button Tl. This breaks the loudspeaker circuit and drives motor Mt. The motor supply voltage is injected to the grid of a valve 5 and load resistance 31 is connected to the input of a valve 14, while the operating winding 26 of the brake magnet is short-circuited. The motor drives at high speed until contact 1 and the button T1 short circuit the coupling magnets K1 K2 so as to reduce the driving speed. In this condition and when the operated button T1 and contact II connect to contact a of relay A the operation of this relay operates the brake and de-energizes the motor. Relay A is operated by rectified and amplified voltage applied to the valve 5 from the motor supply when a signal is correctly tuned. This voltage modulated on the intermediate frequency applied to diode 9-10, produces voltage across resistance 30 to bias diode 33-10 fed by highly selective circuit 35 so that the output at mains frequency is applied to the valve 14 from load resistance 31 only when correct tune is reached. If the required station is not operating the tuning means continue to drive through 360 degrees when a signal lamp may be operated. Holding means may be provided to avoid movement of the tuning members after the disappearance of the controlling voltages in the tuned-in position. Speed reduction is effected by modifying the transmission ratio. In the arrangement shown in Fig. 1a speed reduction is effected by differential couplings 43-48 of which 45, 47, and 48 operate as electromagnetic clutches controlled by magnets K1- K4. The high speed drive is through shaft 62 and the slow speed drive through shaft 57. The drive includes a slipping coupling 72 and drives switch discs S1-S3, which control the coupling magnets and ensure that operation of the brake is not effected at high speed. Remote operation is unsatisfactory with the magnet windings in the negative supply, since considerable voltages may occur and the use of a separate supply is wasteful since the set supply no longer serves as the ballast resistance. In a modification Fig. 2 (not shown) this is avoided by feeding the magnet windings in parallel and de-energizing by removing them from circuit instead of by short-circuiting. With this arrangement speed is reduced by gearing and changed by changing the gear by a switching magnet energized just before correct tuning is effected a spring coupling being included in the high speed drive. The latter ensures that the motor when cut out comes to rest before the high-speed driving of the tuning means can commence. Alternatively a commutator motor drive may be employed and the motor speed controlled by series resistance. This control may be by ball governor which is magnetically controlled to change the driving speed, a time switch being provided to limit the period of slow speed drive.